The subject invention relates to a new and improved pivotal adjustment mechanism for the connection between two mutually movable members. More particularly, a pivotal adjustment mechanism is disclosed, particularly adapted to interconnect the seat and base portion of a chair.
In the prior art, a variety of adjustment mechanisms have been developed for use with chairs. Initially, adjustment mechanism for office type chairs were limited to tilt back devices which restrain the pivoting movement of the seat in the rearward direction in response to a user leaning backwards. More recently, there have been developed more sophisticated mechanisms which permit the user to lean in any axis, thereby providing greater support and comfort. These mechanisms also provide torsional restraint in all axes of movement. Such prior art devices are typically used in office type chairs. However, other applications are possible, such as in a boat, enabling a user to sit relatively quietly in place, during a swell, in a desired horizontal position, while the base of the chair shifts in heavy seas. Similarly, advantages are obtained in road vehicles when driving on uneven ground.
One example of a pivotal adjustment mechanism known in the prior art can be found in U.S. Pat. No. 4,185,803, issued Jan. 29, 1980, to Kalvatn. The mechanism in Kalvatn includes a pair of concentric rings which are interconnected, and having a pair of torsion bars individually connected to each ring. The device in Kalvatn is effective to torsionally restrain the movement of a chair in all axes of motion. However, the Kalvatn device requires relatively large diameter rings to achieve a high level of torsional restraint. Accordingly it would be desirable to provide a new and improved pivotal adjustment mechanism providing torsional restraint in all axes while being compact and having a low profile.